.epsilon.-caprolactam is an important material for nylon and the like. One of processes for preparing said caprolactam is liquid-phase catalytic rearrangement of cyclohexanone oxime in the presence of sulfuric acid. Alternatively, gas-phase catalytic rearrangements in the presence of solid acid are proposed, e.g., boric acid compounds (Japanese published unexamined patent application Nos. 37686/1978 and 12125/1971), silica-alumina (British Pat. No. 881927), solid phosphoric acid (British Pat. No. 881926), mixed metal oxides (Journal of the Chemical Society of Japan, No. 1, 77, 1977), Y-zeolite (Journal of Catalysis, 6, 247, 1966) and crystalline aluminosilicate (Japanese published unexamined patent application No. 139062/1982).
Problems encountered are use of a large amount of fuming sulfuric acid, a large amount of ammonium sulfate by-produced and corrossion of apparatuses caused by fuming sulfuric acid, when sulfuric acid is used above. There are no such problems in the alternative processes above in which solid acid is used. However, they have the other difficulties in reaction selectivity of .epsilon.-caprolactam, life of catalyst, production yield per catalyst, conversion rate of oxime etc. For instance, Japanese published unexamined patent application No. 139062/1982 where crystalline alumino-silicate e.g. ZSM-5 having 40-60 of Si/Al atomic ratio is used discloses no selectivity of .epsilon.-caprolactam but that conversion rate of cyclohexanone oxime is said to be quantitative in such a case where weight hourly space velocity (hereinafter referred to as "WHSV") is as low as about 2.5 hr.sup.-1 and life of catalyst is as short as 15-20 hours. The present inventors have repeated the process of the Japanese published unexamined patent application mentioned above to confirm shortness of life of catalyst and low selectivity of .epsilon.-caprolactam, particularly too short life of catalyst and too small selectivity under commercial WHSV, for example, about 10 hr.sup.-1 or higher.